In a situation this specific, it seems to me to be worthwhile to reply exactly once, in order to inform other readers. Don't expect to change the troll's opinion, but making one comment in order to prevent them from accidentally convincing other people seems worthwhile.

So it's not impossible that MysTerri will retract this particular claim, and that's a decent hook for doubting the rest of the theory. Other responses include accusing me of not being an expert (or lying), renouncing respect for physics, or going content-free.

Also, I'm not sure why you reply here rather than in private, given your reasons.